It is well known in the art to use a two stage combustion process is to burn combustible waste materials under substoichiometric conditions. In this kind of process burn down takes place in a first chamber resulting in combustible gases and ash, where the gases are further mixed with air and burned under superstoichiometric conditions in the second chamber.
U.S. Pat. No. 5,941,184 discloses a controlled thermal oxidation process for solid combustible waste comprising a first combustion stage, wherein the waste is burned in a downward direction from top to bottom. The burn down in the combustion stage is supported by a fixed air flow of predetermined volume which is passed from bottom to top of the waste and a modulated air flow of predetermined lesser volume which is passed over the waste and through the combustion flame. The second combustion stage of this process includes combustion of the products from the first stage by exposing them to high temperature conditions for a short period of time under stoichiometric air conditions.